Ken Carslaw, Lindsay Lee, Kirsty Pringle, Carly Reddington and Graham Mann
NCAS-Climate, University of Leeds
Ken Carslaw is Professor of Atmospheric Science at Leeds and an NCAS aerosol scientist
What are the new findings?
We have identified a major and surprising source of uncertainty in how aerosols (small particles in the air) have affected climate over the industrial period. The Intergovernmental Panel on Climate Change (IPCC) has repeatedly identified the cooling effect of pollutant aerosols as the largest uncertainty among the factors (such as greenhouse gases and changes in pollution) that cause climate change. We have calculated that nearly half the uncertainty in what models calculate stems from not knowing what aerosols were like in the pristine atmosphere before industrialisation. By not knowing what the natural atmosphere was like, we can't accurately determine how much humans have changed aerosols.
Why are these findings important?
Having identified a major cause of uncertainty in climate models, we can now define much better measurement strategies to reduce the uncertainty. This is helpful because the large uncertainty in aerosol effects on climate has persisted for over a decade now, and it limits our ability to understand how the climate will respond to manmade factors in future. Our results point to the need for much better measurements of aerosols in pristine regions of the atmosphere, which resemble what the world might have looked like in, say, 1750.
How did we discover this?
We ran a large number of computer model simulations to understand how small changes in all the aerosol processes combine together to affect the uncertainty in how aerosols affect climate. We found that 46% of the uncertainty could be attributed to natural emissions from volcanoes, marine phytoplankton, sea spray and trees.
Above: The model-calculated aerosol forcing (top) and the uncertainty (bottom).
Find out more:
- see www.see.leeds.ac.uk/aerosol
- Take a look at the Journal article
Carslaw et al (2013), Nature, doi:10.1038/nature12674
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